This invention relates to antennas and in particular to an arrangement to electrically down-tilt the electromagnetic wave pattern associated with a transmit antenna array, or electrically re-orient a receive antenna array.
It is sometimes desirable to adjust the orientation of the electromagnetic wave pattern of a transmit antenna array, particularly a downward adjustment, typically 0xc2x0to 15xc2x0below horizontal, when the antenna is located at a higher altitude than other antennas that communicate with the transmit antenna array. The downward adjustment of the radiation pattern alters the coverage area and may enhance communication with mobile users situated in shadowed areas below the transmit antenna array.
Besides actually mechanically tilting the entire antenna assembly, it is known to electrically down tilt the radiation pattern by controllably varying the relative phase or phases between two or more radiating elements of the antenna array.
One known method by which the relative phase between two or more radiating elements can be changed is to change the relative lengths of respective transmission lines connecting the antenna""s common feed point to each element of the antenna array. Typically, various predetermined lengths of jumper cable are provided which are selectively connected between the common feed and each element to obtain a desired down-tilt. The jumper cables include co-axial connectors to facilitate connection. Furthermore, if stripline is used to connect the common feed point to the respective elements of the antenna array, some form of transition means is required to couple the jumper cable""s co-axial connections to the strip line. A disadvantage of this known method is that it is relatively expensive, less reliable and susceptible to the generation of intermodulation products.
Another known method by which the relative phase between two or more radiating elements can be changed is to change the propagation velocity of the transmission line connecting the common feed point to at least some of the elements of the antenna array. Typically, this latter method is achieved by selectively changing the dielectric constant of the transmission line dielectric. If the transmission line is in the form of a conductive strip, the propagation velocity thereof is changed by introducing a dielectric material between the strip and its associated ground plane.
It is, however, well understood that the introduction of dielectric material under such a conductive strip causes the strip""s normal impedance to be disturbed. For example, if a conductive strip having a certain width is spaced above a ground-plane at a certain distance such as to present a 50 ohm impedance, the introduction of dielectric material between the conductive strip and the ground-plane will reduce the value of this impedance to a value that depends upon the effective dielectric constant of the dielectric material. The resulting impedance mismatch would cause a degradation of return-loss performance of the antenna array.
Australian Patent No. 664625 discloses an arrangement of an adjustable phase shifter comprising dielectric phase shifter elements moveably interposed between conductive strips that couple radiating elements, and a common ground plane. The phase shifter elements are of a characteristic configuration which avoids disturbing the normal impedance during adjustment. This known arrangement, however, requires that respective phase shifter elements be located between each active strip line and the conductive ground plane. Such an arrangement imposes constructional disadvantages as well as limitations to the range of phase shift produced, which consequently imposes limits to the range of tilt.
It is an object of the present invention to provide an adjustable phase shifter arrangement of improved simplicity and compactness.
It is a further object of the present invention to provide an adjustable phase-shifter arrangement which allows a single phase-shifter element of relatively small dimensions to adjust the electrical beam tilt of a multi-element antenna array in a simple manner.
It is still a further object of the invention to provide a phase-shifter arrangement which allows a relatively wide range of phase shift.
According to a first aspect of the invention there is provided a phase shifter element comprising a substantially planar conductor means arranged to form at least one signal path, the at least one signal path including a signal input means at one end thereof, a signal output means at the other end thereof and an intermediate section of conductor, the conductor means being supported in a substantially parallel relationship with a conductive ground plane member, wherein the phase shifter element further includes a planar dielectric member adjacent the conductor means such that the conductor means is between the plane of the dielectric member and the ground plane, and a variable adjustment means arranged to selectively produce relative movement between the conductor means and the planar dielectric member in a direction which traverses the intermediate section of the conductor means, the phase of a signal at the signal output means being determined by the extent to which the planar dielectric member overlaps the conductor means, such overlap being varied by the relative movement.
According to a second aspect of the invention, there is provided a phase shifter element comprising a transmission line means formed by a planar first dielectric member having a first surface opposite a second surface, the first surface supporting thereon a pattern of at least one conductive track arranged to form a signal path of a predetermined physical length, the at least one signal path including a signal input means at one end thereof, a signal output means at the other end thereof and an intermediate section of conductive track, the transmission line means being supported in a substantially parallel relationship with a conductive ground plane member, the ground plane member being spaced from or contiguous with the dielectric member""s second surface, wherein the phase shifter element further includes a second planar dielectric member adjacent the first surface of the first dielectric member, and variable adjustment means arranged to selectively produce relative movement between the first and second dielectric members in a direction which traverses the intermediate section of the at least one conductive track, the phase of a signal at the signal output means being determined by the extent to which the second dielectric member overlaps the pattern of the at least one conductive track, such overlap being varied by the relative movement.
According to a third aspect of the invention there is provided a phase shifter element comprising a transmission line means formed by a planar first dielectric member having a first surface opposite a second surface, the first surface supporting thereon a pattern of at least one conductive track arranged to form a signal path of a predetermined physical length, the path including a signal input means at one end thereof, a signal output means at the other end thereof and an intermediate section of conductive track, the transmission line means being supported in a substantially parallel relationship with a conductive ground plane member, the ground plane member being spaced from or contiguous with the dielectric member""s second surface, wherein the phase shifter element further includes a second planar dielectric member adjacent the first surface of the first dielectric member, the second planar dielectric member including at least two opposite edges, and variable adjustment means arranged to selectively produce relative linear movement between the first and second dielectric members in a direction which is transverse the intermediate section of the at least one conductive track, the phase of a signal at each of the signal output means being determined by the extent to which the second dielectric member overlaps the pattern of the at least one conductive track, such overlap being varied by the relative linear movement.
Preferably, the variable adjustment means comprises an arrangement of the second planar dielectric member slidably fixed adjacent the first surface of the first planar dielectric member, the phase of a signal at the signal output means being determined by the extent to which the second planar dielectric member overlaps the pattern of the conductive track(s), such overlap extent being varied by linear movement of the second planar dielectric member.